1. Technical Field
The present invention relates to a refrigerant, and more particularly to a refrigerant used to effect cooling by utilization of an endothermic action produced upon mixing of two or more constituent components.
2. Background Art
As simple cooling materials which need no electric sources, a cold accumulator using such substances as having large heat accumulating capacity, and a refrigerant utilizing an endothermic action produced upon mixing of two or more constituent components have conventionally been known. Those materials have recently become popular as means for simply cooling human bodies, food products, etc. Among them, the former cold accumulator is inconvenient in that it must be kept in a refrigerator or freezer for cooling before use. On the other hand, the latter refrigerant has an advantage that a cooling effect can be obtained just by mixing at least two kinds of constituent components without requiring any cooling operation in advance.
Such a refrigerant is given by a combination of an inorganic salt, such as an ammonium salt or alkaline metallic, and water, a combination of an inorganic salt and a salt hydrate holding crystal water, or a salt hydrate combined with water. Examples of the inorganic ammonium salt are an ammonium nitrate, ammonium chloride, ammonium sulfate and ammonium bromide. As examples of the salt hydrate holding crystal water, there are conventionally known a 10-hydrate of sodium carbonate, a 7-hydrate of sodium carbonate, a 10-hydrate of sodium sulfate, a 12-hydrate of disodium phosphate, etc.
The refrigerants using crystals of salt hydrates have a little higher cooling effect than the refrigerants using water. Further, the former has no fear of breakage of bags in which the refrigerant is contained, and also has a higher degree of safety in handling. However, that refrigerant has not been satisfactory from the standpoint of practical use for the following reasons. The attainable cooling temperature is on the order of -10.degree. C. at maximum. Where the atmospheric temperature is in excess of 40.degree. C. during storage within warehouses in the summer season, the salt hydrates are melted and, therefore, the endothermic amount obtainable in use is reduced to a large extent. When the atmospheric temperature is lowered again after the melting, the salt hydrates are recrystallized into the form of aggregates. Accordingly, even if the recrystallized salt hydrates are mixed with ammonium salts, the expected cooling effect can no longer be attained.
As salt hydrates which will not melt even under the atmospheric temperature beyond 40.degree. C., there are known a 9-hydrate of sodium methasilicate, a 6-hydrate of magnesium chloride and a 10-hydrate of sodium tetraborate, for example. However, those salt hydrates except for the 9-hydrate of sodium methasilicate hardly exhibit an endothermic action when mixed with ammonium salts. Although the 9-hydrate of sodium methasilicate exhibits a relatively satisfactory cooling effect when mixed with an ammonium salt, there accompanies a shortcoming as follows. Because the reaction between the 9-hydrate of sodium methasilicate and the ammonium salt is slow when the former is used solely, the temperature in a central portion is lowered, but the temperature in an outer wall portion is not so lowered if both the constituent components are accommodated in a bag or container. As a result, it is difficult to make users feel cool satisfactorily in practical use. Thus, to date, there has not been obtained a refrigerant which develops a great cooling effect, shows no melting of crystals even at the high atmospheric temperature on the order of 40.degree. C., and can make users feel cool satisfactorily.
Meanwhile, the refrigerants using water have such an advantage that the water and the other constituent component can be easily mixed with each other and the cooling effect is rapidly developed in the beginning stage. However, the combination of an inorganic salt and water has not been alone satisfactory from the standpoint of practical use for the reasons that the cooling capability is low and a sufficient cool feeling cannot be obtained especially when it is used under the high atmospheric temperature above 30.degree. C.